Over time, engineers have come to recognize that undesirable engine emissions can often be reduced by providing for a more abrupt end to each injection event. In other words, undesirable soot, NOx and noise emissions can usually be reduced at most engine operating conditions when the injection flow rate curve at the end of an injection event is nearly vertical. The prior art is replete with a wide variety of methods and means for providing more abrupt ends to injection events for the many types of fuel injectors currently known. For instance, one known method of seeking a more abrupt end to an injection event is to provide a means for spilling fuel pressure at the end of an injection event in the hopes of hastening the closure rate of the needle check valve, which opens and closes the nozzle outlet of the fuel injector. In another example, some fuel injection systems seek a more abrupt end to an injection event by applying hydraulic fluid pressure to an upper end of the needle valve member in the hopes of hastening its closure rate at the end of an injection event.
The present invention is directed to these and other problems associated with providing a more abrupt end to injection events in hydraulically-actuated fuel injectors.